1. Field of the Invention
The present invention relates broadly to shaped, consolidated siliceous bodies and, more especially, the process for their production. Additionally, the present invention relates to the utility of such shaped articles in the areas of catalyst carriers, absorbents, and in chromatography.
2. Description of the Prior Art
The broad utility, and importance, of siliceous bodies and, particularly those having specific surfaces (measured in terms of m.sup.2 /g), are well known in such fields as adsorption and catalysis. Moreover, numerous conventional methods are employed in the manufacture of these articles, particularly involving the shaping of oxides or hydroxides. For example, it is generally known to agglomerate, by compression or extrusion, powders or finely divided grains of these oxides or hydroxides to yield a desired shape. Similarly, other conventional methods rely upon the gelling of drops of sols of the appropriate oxides or hydroxides in liquids which are substantially immiscible with water. As used in this specification, and in the claims, the term "substantially immiscible with water" is meant to include those liquids which are either immiscible, or only slightly miscible, with water.
Articles obtained by the gelling of silica sol drops are observed to have adequate surface properties and are suitable for use in conjunction with processes conducted in fluidized beds where these particles exhibit a remarkable wear resistance. Typically, in these environments, the dimensions of the bodies do not exceed something on the order of 1 mm.
Larger, hard and wear-resistant, bodies may similarly be obtained by the gelling process; however, these larger bodies suffer a significant disadvantage resulting from the creation of internal stresses, postulated to arise from excessively rapid changes in the water content of the medium into which the bodies are dropped. Accordingly, inferior catalysts are obtained when these larger bodies are, for example, impregnated with various conventional compounds for this purpose. Similarly, mechanical integrity or solidity is observed to be substandard, rendering these larger bodies unsuited for numerous applications.
Bodies obtained by agglomerating, by compressing, or by extruding fresh silica gels, although likely to have surface properties suitable for many uses, often exhibit reduced and substandard mechanical strength precluding their use for many purposes. Depending upon the nature of these bodies, the inherent degradation results in fracture or excessive wear through frictional contact. Various methods have been proposed, and employed, with an eye toward improving the mechanical properties of these bodies, particularly by the addition of bonding agents in the form of clays, sodium silicate, or silica sol. However, although some progress has been achieved in improving mechanical properties, the mechanical strength of these bodies remains substandard for numerous applications.
Accordingly, the need exists to produce agglomerated or consolidated siliceous bodies of large dimensions which do not suffer the significant disadvantage of poor mechanical strength but, on the contrary, exhibit improved mechanical properties. Additionally, the need exists to produce such bodies without the requirement of adding various additional bonding agents and which are adapted for further impregnation without suffering mechanical degradation or deterioration.